Non-volatile memory devices are an important and growing segment of the electronics industry. Non-volatile memory devices retain data or program information without the sustained application of power to the device. Electrically reprogrammable non-volatile memory devices allow the user to change the contents of the memory and retain that information after power is removed from the device: examples are electrically-erasable programmable read-only memory (EEPROM), and flash memory. Flash memory circuits enjoy lower costs than EEPROM since the number of transistors required to execute the memory function is reduced by a configuration which erases large (more than one bit) blocks of the memory in parallel or in a "flash."
Flash memory is a very rapidly growing segment of the microelectronics industry with applications in almost all types of electronic products and systems. For mass memory applications the cost of the memory function is very important. Increasingly, flash memory is employed in what has been termed "embedded" applications where the nonvolatile memory function is incorporated into some other kind of chip, such as a microcontroller, digital signal processor (DSP), disc drive controller, or the like. This embedded approach can improve overall system performance, reduce size and costs by eliminating the need for two separate chips.
Flash memory devices have increased value added in these embedded or highly integrated applications. However, traditional flash memory devices and manufacturing methods present challenges for embedded applications. Typical flash memory cells switch information more slowly than similar CMOS ROM cells. This means that either flash memory must be supplemented by faster-switching volatile memory or the system performance must be slowed to the point where flash memory can keep up. In addition many flash memory devices require greater than 30% increases in manufacturing steps when compared to typical CMOS devices.
A flash memory device which offers high performance in switching speed with rates close to that of standard CMOS would be of great benefit to embedded applications. Two significant embedded applications where flash memory speed directly affects throughput or chip speed are DSP and microcontrollers.